Process for the manufacture of crystalline ammonium sulfite monohydrate



Jan. 19, 1954 v D. A. sKlNNER 2,666,687 Vf PROCESS FOR'THE MANUFACTURE OF' CRYSTALLINE f AMMONIUM SULFITE MONOHYDRATE Filed Nov. l, 1948 v/2 A /M/ /J H20 ATTO/(AMY.

atented jan. 19, 12954 PROCESS FOR THE vMANUFACTURE OF CRYSTALLINE AMMONIUM SULFITE MONOHYDRATE Davis A. SkinneigCompton, Calif.,V assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California f Application November 1, 1948, Serial-No. 57,801

' 4 Claims.

1 .Y This invention relates to the manufacture of ammonium sulfite, and in particular concerns an improved process for preparing pure crystalline ammonium sulte from sulfur dioxide and ammonia. v k f Ammonium sulte is readily formed by reaction between sulfur dioxide and ammonia in the presence `of water, the reaction being effected simplyby passing sulfur dioxide gas into aqueous ammonia, whereby the ammonium sullte is obtained in the form of an aqueous solution. By adding methanol or other water-miscible organic solvent `to such solution, the ammonium sulfite may be caused to crystallize out of solution in the i'ormV of its monohydrate, (NHUzSOe-HZO. However, the use of organic solvents inthis manner to precipitate theammoniumv sulte is not commercially feasible because of the expense involved in dehydratng the mother liquor to recover the organic solvent for re-use in the'process. Similarly, recovery of the ammonium sulte from the aqueous solution by evaporating oi the water is not satisfactory since a considerable portion of the ammonium sulfitebecomes decomposed duringthe evaporation operation. Moreover, evaporation processes in generallare disadvantageous in that they require the expenditure of large amounts of heat, and are no t particularly adapted to continuous operation. 1

y It is accordingly an object of the present invention to provide an improved process for the manufacture of crystalline ammonium sulte.

l' Another object isto provide an ammonium sulfite process which does not require the use of evaporators or organic solvents for` recovering the ammonium sulfte product in crystalline form.

A further object is to provide an ammonium sulte process which is adapted for continuous operation. A

Other and related objects will be apparent from the following detailed description of the invention, and various advantages not specifically referred to herein will occur to those skilled in the art upon employing the invention in practice.

y I have now found that the above objects and attendant advantages may be realized in aprocess whereby ammonia and sulfur'` dioxide are causedrto react in the presence of water to form an aqueous solution of ammonium sulte in the usual manner, and such solution is thereafter treated alternately with ammonia and sulfur dioxide to effect respectively crystallization of ammonium sullte monohydrate and formation offurther amounts of ammonium sulte in disy 2. Treatment of such solution with ammonia whereby the ammonium sulte is precipitated out of solution in the form `of its crystalline monohydrate. 1

3. Separation ofthe crystallized ammonium sultemonohydrate from themother liquor'by ltering,.centrifuging:or other suitable operation.

4. Dilution of the mother liquor with sufficient water to replace that used in the formation of the ammonium sulte monohydrate. Y

5. Treatment of .the` diluted mother liquor, which contains dissolved` ammonia as a result'of step 2, with sulfur dioxide whereby further quantities of ammonium sulfite are formed as in step l. f t

It will be readily vperceived that this sequence of operationsreturns the system to the condition f prevailing at the end of'step 1, and that by repeating steps 2 to 5 in sequence the process may be carried out for as long as may be desired. lIf continuously operating means are employed for separating the crystallized ammonium sulte monohydrate from themother liquorv in step 3, i. e., a rotary-type filter, the process may be operated continuously since the other. steps merely involve the addition. of liquids or gases.

The invention may be more readily understood by reference to the accompanying drawing, the

single figure of which represents a schematic flow sheet of a preferred mode lof practicing the in- Vention whereby the above sequence of operations is effected in a continuous manner.

Referring now to the drawing, the initial step of the process, i. e., theformation of ammonium suliite in aqueous solution, is conveniently carried out in a reaction tower I0 which may be lled with materials to promote good gas-liquid contact, e. g., bubble-cap plates, Raschig rings, porous tiles, etc. Water is introduced into the top of the reaction tower through lines Il and Ila at a rate controlled by valve l2. Within the towerthe stream of Water may be broken lup into accese? er I0, the ammonia and sulfur dioxide gases rise`r` fur dioxide, or any inert gases which may be pres-` ent, are discharged from the top of the tower through line I'I to waste or to suitable facilities fQr recvering useful @meneurs- The. aqueous ammonium elle@ is Withdrawn from the bottm Of the iet/sf through line l@ and passed t ,Cry-r tallizer I9 which take the form of a simple closed vessel or tanti. Ammonia o r an ammoniacontainin'g gas is introduced into the crystallizer through wline 2D at a rate controlled by yvalve 2| in such manner that it is intimately contacted with the m1160111? ammonium Sulte Salaten. As the liquor within the crystallizer becomes more and more saturated with ammonia, the ammonium sulte precipitates out of solution as crystalline ammonium sulte monohydrate. In order to promote, good absorption of the ammonia in the` ammonium sulte. liquor, the crystallizer may `advantageously be lequipped with a stirrer or otherv agitating means. Any ammonia not absorbed within .the crystalli'zer is led off through line 22 and recirculated. The ammonium suliite monohydrat'e crystalsA in the form of a slurry in concentrated aqueous ammonia vare withdrawn from the crystalli-zer through line 23 and are passed to a continuous filter .24 where they are separated trom the mother rliquor and passed to lsuitabledrying and storage facilities, not shown; The motherliquor leaving the filter through line 25, and comprising a concentrated aqueous solution of ammonia saturated with ammonium sul# iite, is passed to a storage rtank from which it is withdrawn through line 2'I at a rate controlled by valve 28 to be recycled back to the top of re-A action tower IU. through lines y29 and I-Ila.A Dilution `ofthe ammoniacal recycle liquor occurs in line I Iciy where it is 'mixed with the water' enter-- ingv the system through line lI I.

`When the .above-described process is initiated, all of the ammonia used informing the ammonium sulte enters the system near the bottom of the reaction tower through line I3 and valve I4. Similarly, the amount of waterintroduced into the top of the tower viva line II vand valve I2- is in excess of that required for the formation of the ammonium suliite. As the Vprocess continu'es, however,v ammonia becomes supplied to the tower in the form ofthe aqueous ammoniacal recycle liquor, so'that veventually the quantity of ammoniar'supplid directly to tlie tower may vert" drastically be" reduced or even entirely cut; off, 4substantially all of the ammoniaJ entering into the reaction being introduced into the system atA the crystallizer wherev it is initially employed to. precipitate the ammonium sulte monoliydrate. Similarly, o nce a steady cycle has'been established the amount of- 'water supplied 'to the system may be reduced to the quantity actually used up in the reaction plus a small additional quantity to make up for handling losses.

It will be apparent from the above that the process of the invention is highly eflicient in that the only materials supplied to the process arey those which actually enter-the reaction by which the desired product is formed. The entire process may be carried out at room temperature without the expenditure of heat. Recovery of the ammonium sulilteproduct from the aqueous solution in which it is initially obtained is accom- .plish'ed without the use of extraneous precipitathis ne product is recovered as a matter of course and employed in the formation of more product. Similarly, the ammonium sulfite which saturates the mother liquor leaving the filter is entirely recovered since all of such liquor is recycled baci; to the reaction zone. Even the water is employed only the amount required by the reaction.

inasmuch as the present process involves the absorption of gases in liquids, it is desirable that it be carried out at as low a temperature as may be convenient.V The reaction between ammonia, sulfur dioxidel and water in the reaction tower is exothermic in nature, as is the absorption of ammonia in water which occurs in the crystallizer. Accordingly, it is usuallyv desirable that means be, provided for withdrawing heat'from the system at either orV both of these points. ySuch means may comprise internally cr externally disposed coils through which Water is circulated. Alternatively, the`A gases introducedinto the reaction tower and the crystallizer may beled in at a plurality of points in 1order to` secure amore even dissipation vof the heat.

The rates at which the reactants are introduced into the system may be varied between wide limits. However, since it is desirable to suppress the formation of ammonium acid -sullite, (NHDHSOS, and ammonium polysulte, (NHQzSzOaan excess,v of ammonia is maintained in the system. Since Aall of they ammonia is re-v cycled within the system, no loss occurs through the use oit such excess. The presence of Aexcess ammonia is further advantageous in that itfsuppresses corrosion of the equipmentlby the acidic sulfurdioxide. As 'previously stated, water is employed in an amount sutlicient to replace that used up in the Yformation of the ammonium suliite'menohydrate plus enough to make up for losses, e. g., the water iost by adherence to the crystalline product taken from the filter.

While the process has herein been described as being carried out in a continuous manner, it will be understood that it is equally well vadapted to semi-continuous or batch-wise operation. rIglius, for example, sulfur dioxide may vbe absorbed in ordinary commercial aqueous ammoniav to form an aqueous solutionof ammonium suli'ite which preferably contains from about 20V tov about 30 per lcent by weight of the ammonium suliite. Such solution may then be saturated with :ammonia and Viiltered to separate the am,- rnonilum suliite monchydrate crystals `willich are thereby precipitated, and vthev mother liquor,` which Consists 0f' coflntrated. aqueQus alemania saturated with ammonium suliite, may be passed to storage. When itis desired to'prepare a iurihef Quantity Of ammonium Sulitle., the mother liquor is withdrawn from storage, diluted with water, and treated with` sulfur dioxide asherein explained. ln this way the mother liquor from Vl achpreparation isi-employed as a starting? material'for the next succeeding batch.

The following example is illustrative ofl the practice Soffthe'inventionfbut is not to be construed as limiting the same. All proportions are in parts by weight. v

vEzrample Sulfurdioxide is absorbed in commercial aqueous ammonia toobtainv aqueous ammonium `sul lte analyzing 37.4 per cent by weight of ammonium sulte monohydrate. Approximately 1194 parts of this solution is then treated with gaseous ammonia. During the addition of the ammonia, the temperature increases somewhat Ibut upon cooling crystalline ammonium sulflte monohydrate precipitates from solution. The solution is then filtered whereby there is obtained 377 parts of dry crystalline ammonium sulte monohydrate, representing a recovery of about 84.3 per cent, and 1101 parts of mother liquor consisting of concentrated aqueous ammonia saturated with Yammonium sulfite. The mother liquor is then diluted with about 100 .parts of water, and is treated with about 360 parts of sulfur dioxide to form additional ammonium sulte. By treating the resulting liquor with 210 -parts of ammonia, ammonium sulte monohydrate is precipitated as before and is recovered in the amount of 712 parts by weight. The mother liquor amounts -to about 1058 parts by weight and contains about 32 per cent by weight of dissolved ammonia. It may again be diluted and treated with sulfur dioxide as before to form more ammonium sulflte, and .the process continued indefinitely.

While the advantages of the process of the invention are fully realized in a semi-continuous or batch-wise type of operation. it is preferred to ycarry out large-scale operations in a continuous manner as previously 'described with reference 'to the drawing. Many variations within the scope vof the invention will be apparent to those skilled in the art. Thus, for example, the reaction vessel is not limited to the packed tower type herein described, but may take a variety of other forms. Similarly,Y the crystallizer which has been described as a simple tank, maybe provided, for example, with a conical bottom in which the precipitated ammonium sulte monohydrate crystals lare allowed to settle before being passed to the lter. A large -proportion of the mother liquor may thus be separated from the crystals by simple decantation and passed 'to the storage tank without passing through the lter.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the methods herein disclosed provided the step or steps stated by any of the following claims, or the equivalent of such stated step or steps, be employed.

I, therefore, particularly point out and distinctly claim as my invention:

1. In a process for the manufacture of crystalline ammonium sulte monohydrate, the steps which comprise (1) passing sulfur dioxide into an aqueous alkaline solution containing dissolved ammonium sulfte and ammonia in the substantial absence of gaseous ammonia and in an amount less than that required to react with all of said dissolved ammonia to form ammonium sulite; (2) subsequently passing ammonia into the resulting solution in the substantial absence of" gaseous suuur 'dioxide' and inv an amount Y11i excess of that required to precipitate ammonium sulte monohydrate, whereby there is obtained precipitated crystalline ammonium sulte monohydrate and anl alkaline mother liquor containing' dissolved ammonium 'sulte and; ammonia; (3) separating said crystalline ammonium sulii'te monohydrate from said alkaline mother'liquor; (4) `'diluting said'alkaline -mother liquor; with water; and""(5') returning the diluted"*alkaline mother liquor to step (l).

2. In a process for the manufacture of crystalline ammonium suliite monohydrate, the steps which comprise (1) passing sulfur dioxide into an aqueous alkaline recycle liquor containing dissolved ammonium sulte and ammonia in the substantial absence of gaseous ammonia and in an amount less than that required to react with all of said dissolved ammonia to form ammonium sulite; (2) flowing the liquor so obtained to a precipitation zone wherein 4gaseous ammonia is passed into said liquor in the substantial absence of gaseous sulfur dioxide and in an amount in excess of that required to precipitate crystalline ammonium sulte monohydrate, whereby there is obtained precipitated crystalline ammonium sulfi-te monohydrate and an alkaline mother liquor containing dissolved ammonium sulte and ammonia; (3) separating said crystalline ammonium sulte monohydrate from said alkaline mother liquor; (4) diluting said alkaline mother liquor with water; and (5) returning the diluted alkaline mother liquor -to step (1) as said aqueous alkaline recycle liquor.

3. In a process for the manufacture of crystalline` ammonium sulte monohydrate, the steps which comprise (1) continuously passing sulfur dioxide into an aqueous alkaline recycle liquor containing dissolved ammonium sulte and ammonia in the substantial absence of gaseous ammonia and in an amount less than that required to neutralize said aqueous alkaline recycle l1quor; (2) continuously flowing the liquid so oby tained into a precipitation zone wherein gaseous ammonia is continuously passed into said liquor in the substantial absence of gaseous sulfur dioxide and in an amount sufficient to precipitate crystalline ammonium suliite monohydrate, whereby there is obtained precipitated crystalline ammonium sulte monohydrate and an alkaline mother liquor containing dissolved ammonium sulte and ammonia; (3) continuously separating said crystalline ammonium sulte monohydrate from said alkaline mother liquor; (4) continuously diluting said alkaline mother liquor with an amount of water at least equivalent to that consumed in the formation of the separated crystalline ammonium sulte monohydrate; and (5) continuously returning the diluted alkaline mother liquor to step 1) as said aqueous alkaline recycle liquor.

4. In a process for the manufacture of crystalline ammonium sulte monohydrate, the steps which comprise (l) passing gaseous ammonia into a concentrated aqueous alkaline solution of ammonium sulite in the substantial absence of gaseous sulfur dioxide and in an amount in excess of that required to precipitate crystalline ammonium suliite monohydrate from said solution, whereby there is obtained precipitated crystalline ammonium sulnte monohydrate and an alkaline mother liquor containing dissolved ammonium sullte and ammonia; (2) separating said crystalline ammonium sulte monohydrate mana,J and; in. n$ amount.. Iess than thatdneqpred react. with the. ammonia which contained sali dilutedlvalkaline mother. lhpomrwhereby 10- 452,378.

82: there-isformed avila-@ther quantityr ot, the concenf trated aqueousallkalin slutiqn oi ammonium sulta l mams, A.

` References cited 1n the me ofY this. patent UNITED STATES, PATENTS Numbers Nannev Date:

Lachqmette. qm..- May iflaal 

1. IN A PROCESS FOR THE MANUFACTURE OF CRYSTALLINE AMMONIUM SULFITE MONOHYDRATE, THE STEPS WHICH COMPRISE (1) PASSING SULFUR DIOXIDE INTO AN AQUEOUS ALKALINE SOLUTION CONTAINING DISSOLVED AMMONIUM SULFITE AND AMMONIA IN THE SUBSTANTIAL ABSENCE OF GASEOUS AMMONIA AND IN AN AMOUNT LESS THAN THAT REQUIRED TO REACT WITH ALL OF SAID DISSOLVED AMMONIA TO FORM AMMONIUM SULFITE; (2) SUBSEQUENTLY PASSING AMMONIA INTO THE RESULTING SOLUTION IN THE SUBSTANTIAL ABSENCE OF GASEOUS SULFUR DIOXIDE AND IN AN AMOUNT IN EXCESS OF THAT REQUIRED TO PRECIPITATE AMMONIUM SULFITE MONOHYDRATE, WHEREBY THERE IS OBTAINED PRECIPITATED CRYSTALLINE AMMONIUM SULFITE MONOHYDRATE AND AN ALKALINE MOTHER LIQUOR CONTAINING DISSOLVED AMMONIUM SULFITE AND AMMONIA; (3) SEPARATING SAID CRYSTALLINE AMMONIUM SULFITE MONOHYDRATE FROM SAID ALKALINE MOTHER LIQUOR; (4) DILUTING SAID ALKALINE MOTHER LIQUOR WITH WATER; AND (5) RETURNING THE DILUTED ALKALINE MOTHER LIQUOR TO STEP (1). 